From: | Philip Warner <pjw(at)rhyme(dot)com(dot)au> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)hub(dot)org |
Subject: | Re: COALESCE implementation question |
Date: | 2000-08-06 04:12:38 |
Message-ID: | 3.0.5.32.20000806141238.01ec9580@mail.rhyme.com.au |
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Lists: | pgsql-hackers |
At 23:28 5/08/00 -0400, Tom Lane wrote:
>Philip Warner <pjw(at)rhyme(dot)com(dot)au> writes:
>>> Well, the standard is perfectly clear, isn't it? If V(1) has side
>>> effects then trying to optimize this into just one evaluation of V(1)
>>> will generate non-spec-compliant results.
>
>> At least with the new function manager, if I feel te need I can write a
>> 'CoalesceValues' function (at least for fixed numbers of parameters).
>
>Mmm ... not really. You could detect nulls all right, but a function-
>based version of COALESCE would evaluate *all* its arguments exactly
>once, which is certainly wrong.
Good point. Although in the specific case (two args, one of them constant),
it's not an issue. I guess I'll just have to live with double-evaluation,
and a COALESCE than can return NULL. Grumble grumble...
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